The present invention relates to an ultrasonic endoscope for an ultrasonic diagnosis on a desired region in the body cavity.
In general, ultrasonic endoscopes of this type comprise an operation section and an insertion section extending therefrom to be inserted into the body cavity. A distal member with a scanning chamber therein is attached to the distal end of the insertion section. The chamber is filled with a liquid ultrasonic transmission medium. Also, it contains an ultrasonic generator and a rotating mirror for reflecting, in a predetermined direction, ultrasonic waves generated from the generator. The mirror is rotated by a motor in the operation section. To this end, the motor is coupled to the mirror by a transmission shaft, such as a wire, which is passed through the insertion section.
The transmission shaft extends into the scanning chamber full of the liquid. In order to prevent the liquid from leaking from the chamber to the insertion section, the periphery of the shaft must be sealed by an O-ring or the like. In this case, however, that portion of the shaft sealed by the O-ring is subject to increased friction, requiring correspondingly greater driving torque. After long use, the O-ring would be deteriorated to have its sealing capability reduced. Consequently, the liquid in the scanning chamber would possibly leak from the scanning chamber.